あるV字谷におけるシーティングの力学的背景に関する研究

概要

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There are a considerable number of sheeting joints at a V-shaped valley in Japan, which is a construction site for a P-Dam. Sheeting joints could cause water leakage and reduce the strength of rock mass as a dam foundation. The mechanical backgrounds of sheeting joints were therefore investigated. In-situ stress measurement by the stress relief method revealed that maximum horizontal stress, which is almost perpendicular to the P-River, is about 12 MPa. This result coincides with results obtained by the Deformation Rate Analysis method. It was also clarified that the temperature in rock mass shows large day-variation as deep as 30 cm, and that a significant temperature gradient appears under direct sunlight. Through numerical analyses, it was determined that an inclined crack near a free surface can grow much longer than that in an infinite medium. From these points of view, it was considered that the sheeting joints are exfoliation as a result of crack propagation near the free surface under horizontal stress concentrated by the geometry of the V-shaped valley and periodically-acting horizontal thermal stress.
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